1. Field of the Invention
The present invention relates to a substrate for an ink jet recording head (referred to as “ink jet recording head substrate” hereinafter), which is used in an ink jet recording head for performing a recording operation by discharging an ink droplet from a discharge port and which includes an electro-thermal converting element for generating discharging energy, a switching element for driving the electro-thermal converting element and a logic circuit for controlling the switching element, an ink jet recording head having such an ink jet recording head substrate, and an ink jet recording apparatus using such an ink jet recording head.
2. Related Background Art
In accordance with an ink jet recording method for discharging ink from a discharge port by utilizing heat, an ink jet recording apparatus used as terminals for generating various outputs may include an ink jet recording head mounted thereon. The ink jet recording head includes an ink jet recording head substrate on which electro-thermal converting elements (heaters), elements for switching the electro-thermal converting elements (referred to as “switching elements” hereinafter) and logic circuits for driving the switching elements are commonly formed.
FIG. 21 is a schematic sectional view showing a portion of a conventional ink jet recording head. On a semiconductor substrate 901 formed from mono-crystal silicon, there are formed a p-type well area 912, an n-type drain area 908 having high impurity density, an n-type electric field relieving drain area 916 having low impurity density, an n-type source area 907 having high impurity density and a gate electrode 914, which constitute a switching element 930 utilizing an MIS-type electric field effect transistor. Further, on the surface of the semiconductor substrate 901, there are formed a silicon oxide film as a heat accumulating layer 917 and an insulation layer, tantalum nitride film as a heat-resistive layer 918, an aluminum alloy film as wirings 919 and a silicon nitride film as a protection layer 920. In this way, a substrate for the recording head. Here, a heat generating portion is designated by the reference numeral 950 and ink is discharged from an ink discharge portion 960 opposed to the heat generating portion 950. Further, a top plate 970 cooperates with the substrate to define a liquid path 980.
By the way, with respect to the recording head and the switching element having the above-mentioned constructions, although many improvements have been made, in recent years, as for the article or product, there have been requested a need for a high speed driving ability (arrangement of a larger number of electro-thermal converting elements), an energy saving ability (enhancement of an electric power consuming ratio at the electro-thermal converting element; high voltage driving), a high integrating ability (enhancement of arranging density of electro-thermal converting elements and switching elements arranged in parallel therewith), low cost achievement (enhancement of the substantial number of chips per one wafer by making a chip size smaller by reducing a size of the switching element per one electro-thermal converting element; identical voltage between motor power supply voltage (for example, 20 to 30 V) of main body and electro-thermal converting element driving voltage) and a high performance ability (enhancement of pulse control by performing high switching).
However, under a circumstance where large electric current is required for driving the load such as the electro-thermal converting element, if the conventional MIS-type electric field effect transistor 930 is operated, a pn reverse bias joint portion between the drain and the well cannot endure the high electric field to generate leak electric current, with the result that withstand voltage requested for the switching element cannot be satisfied. Further, if ON resistance of the MIS-type electric field effect transistor used as the switching element is great, due to useless consumption of the electric current, there arises a problem to be solved that the electric current required for driving the electro-thermal converting element cannot be obtained.
To the contrary, there has recently been proposed a technique in which DMOS (dual diffusion MOS) transistor which can be made small-sized is used as a driver. However, as will be described later, although the DMOS transistor has high drain withstand voltage, withstand voltage between the source and the substrate is not so high. Thus, in a case that the DMOS transistor is used as the switching element for the electro-thermal converting element, due to increase in source voltage caused by the product of the electric current flowing through the electro-thermal converting element and ground wiring resistance, break-down may occur between the source and the substrate.
Therefore, an object of the present invention is to provide a DMOS transistor capable of flowing large electric current and capable of obtaining high withstand voltage, high speed driving, energy saving and high integrating ability and capable of achieving low cost of entire recording apparatus and to provide means for preventing break-down between a source and a substrate which must be considered in a case where the DMOS transistor is used as a switching element for an electro-thermal converting element.